Effect of Rare Earth on Cyclic Oxidation Resistance of Cast High Speed Steel Rolls

The cyclic oxidation experiments on cast high speed steel roll added rare earth elements were using thermal gravimetric analyser. The structure morphology observation, phase analysis, chemical component analysis and cast on oxide films after cyclic oxidation carried out, adopting SEM, XRD, EDS, respectively. The results show that the cyclic oxidation possesses a characteristic, i.e. oxidized selectively on matrix and carbide, formed oxide film M_2O_3 which contain different alloying elements on matrix and carbide, the oxides formed on the carbides are higher. Oxide grain size growing with cyclic oxidation temperature increasing, the oxidation kinetic curve conforms to the parabola law. Rare earth elements can increase cyclic oxidation resistance of high speed steel, porosity of high speed steel oxide films is lower than non-added rare earth element steel, oxidation occurs selectively on carbide particles of rare earth elements which contains Ce, La, etc., formed similar “nail” granular oxide-which fixes oxide film to matrix, and strengthens adherence of oxide film that is not easy to drop-out. This is one of the systems to increase oxide film adherence.